GB2217846A

GB2217846A - Pressure sensor

Info

Publication number: GB2217846A
Application number: GB8809617A
Authority: GB
Inventors: Aubrey Michael Crick
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1988-04-22
Filing date: 1988-04-22
Publication date: 1989-11-01
Also published as: GB8809617D0

Abstract

A pressure sensor, e.g. for use in a cylinder of an internal combustion engine, has a flexible diaphragm 12 responsive to changes in pressure. The diaphragm is protected by a heat shield 14 having openings 16 whereby pressure is transmitted to the diaphragm 12. <IMAGE>

Description

PRESSURE SENSOR.

This invention relates to pressure sensors e.g.

for effecting cylinder pressure measurements on internal combustion engines.

A number of transducer devices have been described for the measurement of pressure under hazardous conditions such as those pertaining in a cylinder of an internal combustion engine. A recent development has been the introduction of a transducer in which the pressure responsive element comprises a flexible element formed from single crystal silicon. In one form of this transducer the silicon transducer element is protected from exposure to the cylinder gases by a flexible metal diaphragm. Movements of the diaphragm in response to cylinder pressure changes, i.e.

during a four stroke or two stroke cycle, are transmitted to the silicon element via a push-rod coupled therebetween. Such an arrangement is described in our publication specification No. 2, 175, 398 (A.M.

Crick 20). Whilst this structure is generally successful in operation, we have found that, under some conditions, the high temperatures generated in the cylinder can cause destruction of the diaphragm.

The object of the present invention is to minimise or to overcome this disadvantage.

According to the invention there is provided a pressure sensor device adapted for use under high temperature conditions, the sensor including a flexible diaphragm which, in use, is exposed to the source of pressure, means for determining displacement of the diaphragm responsive to said pressure and a heat shield exposed to the source of pressure and adjacent the diaphragm so as to conduct heat away from the diaphragm, said shield having one or more openings whereby pressure is transmitted from the pressure source to the diaphragm.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional view of a pressure sensor; and Figure 2 is a sectional view of an alternative pressure sensor.

Referring to Figure 1, the pressure sensor includes a generally tubular e.g. metal body 11 one end of which is closed by a flexible diaphragm 12. Typically the diaphragm 12 is formed from stainless steel and is welded to the end face to the tubular body 11 as to provide a pressure tight seal.

The diaphragm 12 abuts a push rod assembly 13 whereby displacement of the diaphragm in response to a pressure applied thereto is transmitted to a transducer (not shown) whereby an electrical signal indicative of that displacement is generated. Protection of the diaphragm from excessive heat is provided by a generally cup-shaped heat shield 14 advantageously formed from stainless steel. The shield is attached to the rim of the diaphragm 12 e.g. by welding so as to define a cavity 15 therebetween. Openings 16 are provided in the shield 14 to allow pressure changes adjacent the outer surface of the heat shield 14 to be transmitted to the diaphrqagm 12 via the cavity 15.

In use the sensor of Figure 1 may be inserted in an opening in a cylinder head of an internal combustion engine such that the end of the sensor bearing the heat shield 14 is exposed to the cylinder gases. Heat from these gases is conducted via the shield 14 to the sensor body ill and thence to the cylinder head thus protecting the diaphragm 12 from exposure to excessive heat.

An alternative sensor construction is shown in Figure 2 of the accompanying drawings. This sensor has a generally tubular body 21 having an increased diameter end portion 22 defining a shoulder 23. A tubular insert 24 having an increased diameter end portion 25 is located in the body 21 with the end portion 25 abutting the shoulder 23. The insert supports a push-rid assembly 26.

A diaphragm 27, typically of stainless steel, is located in the increased diameter portion 22 of the body 21 and is enclosed by generally cup-shaped heat shield 28 provided with openings 29. In some applicatioms the heat shield may comprise a metal gauze.

The heat shield and diaphragm are retained in abutment with the insert 24 by rolling or crimping of the body portion 22 to form an inwardly directed retaining lip 30. The diaphragm 27 has a profiled centre protion 27a for receiving one end of the push-rod assmebly 26 whereby displacement of the diaphragm in response to a pressure applied thereto is transmitted to a transducer (not shown). Typically the transducer comprises a piezo-resistive device formed by selective etching from a unitary body of single crystal silicon.

The assembly of Figure 2.is inserted in an opening 31 in a cylinder head 32 of an internal combustion engine and is retained therein by a threaded tubular member 33. A gasket 34 provides a seal between the sensor and the cylinder head, As before, the heat shield conducts heat away from the diaphragm region, but allows transmission of cylinder pressure to and from the diaphragm.

The sensors described herein are intended for use in vehicle engines, but they may also be employed in other applications requiring exposure to a hostile enviroment.

Claims

CLAIMS.

1. A pressure sensor device adapted for use under high temperature conditions, the sensor including a pressure responsive element, and a heat shield disposed adjacent the element whereby heat is conducted away from the element, said heat shield having one or more openings whereby the element is exposed to said pressure.

2. A pressure sensor device adapted for use under high temperature conditions, the sensor including a flexible diaphragm which, in use, is exposed to the source of pressure, means for determining displacement of the diaphragm responsive to said pressure and a heat shield exposed to the source of pressure and adjacent the diaphragm so as to conduct heat away from the diaphragm, said shield having one or more openings whereby pressure is transmitted from the pressure source of the diaphragm.

3. A pressure sensor as claimed in claim 2, wherein the sensor has a tubular body having an inwardly crimped lip portion in which the diaphragm and shield are retained.

4. A pressure sensor as claimed in claim 2, wherein the heat shield is welded to the diaphragm.

5. A pressure sensor as claimed in claim 1, 2, 3 or 4, wherein the heat shield is formed from stainless steel.

6. A pressure sensor as claimed in any one of claims 1 to 5, wherein the heat shield comprises a metal gauze.

7. A pressure sensor substantially as described herein-with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.

8. An internal combustion engine provided with one or more sensors as claimed in any one of claims 1 to 7.

9. A vehicle having an engine as claimed in claim 8.